Display device

ABSTRACT

A display device includes a display part; a driving part; and a display control part, the display control part being configured to provide a transition period between first and second driving periods in switching from the first driving period to the second driving period, the first driving period allowing the display part to be driven at a first frame frequency, the second driving period allowing the display part to be driven at a second frame frequency, the transition period including a period where the display part is driven at at least one frame frequency with a value between the first and second frame frequencies, the transition period including positive and negative periods that last for different total durations, the positive period allowing the display part to be driven at a positive voltage, the negative period allowing the display part to be driven at a negative voltage.

TECHNICAL FIELD

The present invention relates to display devices. More specifically, thepresent invention relates to alternating current (AC) driven displaydevices.

BACKGROUND ART

Display devices such as liquid crystal display devices are used inapplications such as TVs, smartphones, tablet PCs, PCs, and automotivenavigation systems. In the field of display devices for mobileterminals, particularly, low power consumption is required as well asimproved display quality and thus various techniques have been proposed(e.g., Patent Literatures 1 to 3).

CITATION LIST Patent Literature

-   Patent Literature 1: JP 2001-312253 A-   Patent Literature 2: JP 2015-75723 A-   Patent Literature 3: WO 2013/115088

SUMMARY OF INVENTION Technical Problem

Even in a conventional display device that causes no flickers in a modeproviding moving images and a mode providing still images, flickersstill may occur when the frame frequency is changed between a movingimage and a still image, leading to deteriorated display quality. Thepresent inventor made various studies to find the causes of this, whichare described in the following referring to a liquid crystal displaydevice as an example.

In a liquid crystal display device, continuous drive at direct currentvoltage (DC voltage) causes accumulation of charge or chemical reaction(e.g., redox reaction) in members such as a liquid crystal layer (liquidcrystal material) and an electrode to deteriorate the displayproperties. In response to this, a driving method is typically employedin which the polarity of applied voltage is alternately switched betweenpositive and negative polarities for each frame, whereby direct currentvoltage component applied to the liquid crystal layer is made almostzero. Unfortunately, in the case where the liquid crystal layer (liquidcrystal molecules) shows different response performance depending on thepolarity of the voltage applied (positive voltage or negative voltage),even when the positive and negative voltages applied to the liquidcrystal layer have the same absolute value, the light transmittances ofthe liquid crystal layer corresponding to these voltages are differentfrom each other. This unfortunately provides images with variedluminances, leading to flickers due to the variation in brightness foreach frame. Accordingly, in order to make the light transmittance of theliquid crystal layer constant for each frame, the positive and negativevoltages (absolute values) applied to the liquid crystal layer, whichare substantially equal to each other, is shifted to have differentabsolute values. This shifting can be achieved by adjusting the positiveand negative voltages (absolute values) or adjusting the voltage appliedto the common electrode (hereinafter, also referred to as commonvoltage). This enables the liquid crystal layer to have an almostconstant light transmittance, leading to minimized flickers. The commonvoltage that has been adjusted to minimize flickers is also referred toas an “optimized common voltage”. The optimized common voltage enablesthe liquid crystal layer to have a constant light transmittance (enablesimages to have a constant luminance) in both cases of applying positiveand negative voltages, thereby reducing flickers to an allowable level.

Even when flickers are minimized to be unrecognizable, flickers may beobviously recognized in the following case. That is, when changing theframe frequency, the voltage applied to the liquid crystal layer may betemporarily unbalanced depending on the balance of RC time constantbetween members such as the liquid crystal layer, an alignment film, andan insulating film. The temporary changes in the optimized commonvoltage (Vcom) for minimizing flickers possibly cause obvious flickersafter changing the frame frequency. The phenomenon the optimized commonvoltage unintendedly changes for some reason is also referred to as“Vcom shift”.

As mentioned above, no measure has been found which enables conventionaldisplay devices to change the frame frequency with reduced flickers.

Patent Literature 1 discloses, as a measure for achieving low powerconsumption, a driving method that provides a pause period where allscanning signal lines are brought to a non-scanning state after ascanning period where the screen is scanned. Unfortunately, PatentLiterature 1 lacks description relating to changing the frame frequency,and thus there is still room for improvement.

Patent Literature 2 discloses a liquid crystal display device thatreduces flickers during low-frequency driving and intermittent drivingand including description regarding the off-leakage current of matrixpatterned thin film transistor elements that control supply of voltageto liquid crystal pixels, the resistivity of liquid crystals, theresistivity of an alignment film, and a relation between the product ofthe resistivity and the capacitance of liquid crystals and the productof the resistivity and the capacitance of the alignment film, and thelike. However, Patent Literature 2 lacks description relating tochanging the frame frequency and thus there is still room forimprovement.

Patent Literature 3 discloses a display device that provides atransition period where the display part is driven at a refresh ratehaving a value between a first value and a second value when switchingthe refresh rate from the first value to the second value. Thetransition period provides a positive period where the display part isdriven at a positive voltage and a negative period where the displaypart is driven at a negative voltage, in substantially the sameproportion as each other. The present inventor conducted intensivestudies on this to found that, unfortunately, in the technique disclosedin Patent Literature 3, when the frame frequency is significantlychanged, the potential of the common electrode takes a long time toreach an optimal position (the position where flickers are minimized),thereby possibly causing flickers. Thus, there is still room forimprovement.

The present invention has been made under the current situation in theart and aims to provide a display device that can change the framefrequency with reduced flickers.

Solution to Problem

The present inventor made various studies on a display device that canchange the frame frequency with reduced flickers and focused on astructure that provides a transition period including a period where thedisplay part is driven at at least one frame frequency between twodifferent frame frequencies when switching between the two differentframe frequencies. Then, the inventor found a structure in which thetransition period includes a positive period and a negative period thatlast for different total durations, the positive period allowing thedisplay part to be driven at a positive voltage, the negative periodallowing the display part to be driven at a negative voltage. Theinventor thereby found a successful measure to the above issue to arriveat the present invention.

In other words, an aspect of the present invention may be a displaydevice including: a display part including a common electrode; a drivingpart configured to drive the display part; and a display control partconfigured to control the driving part, the display control part beingconfigured to perform control for AC drive of the display part, with avoltage applied to the common electrode defined as a reference and toprovide a transition period between a first driving period and a seconddriving period in switching from the first driving period to the seconddriving period, the first driving period allowing the display part to bedriven at a first frame frequency, the second driving period allowingthe display part to be driven at a second frame frequency different fromthe first frame frequency, the transition period including a periodwhere the display part is driven at at least one frame frequency with avalue between the first frame frequency and the second frame frequency,the transition period including, with a voltage applied to the commonelectrode defined as a reference, a positive period and a negativeperiod that last for different total durations, the positive periodallowing the display part to be driven at a positive voltage, thenegative period allowing the display part to be driven at a negativevoltage.

At least one period selected from the group consisting of the firstdriving period, the second driving period, and the transition period mayinclude a frame period including a refreshing period that refreshes ascreen of the display part and a pause period that is longer than therefreshing period and stops refreshing the screen of the display part.

There may be a difference between polarity of the positive period or thenegative period in the transition period, whichever has a longer totalduration, and polarity of a frame period that belongs to the firstdriving period or the second driving period, whichever has a lower framefrequency, and is closest to the transition period.

The number of frame periods in the transition period may be 1.

Provided that F₁ represents the first frame frequency (unit: Hz), F₂represents the second frame frequency (unit: Hz), and F₃ represents theframe frequency (unit: Hz) in the transition period, the framefrequencies may satisfy the following formula (1).

[Math.  1] $\begin{matrix}{0.4 \leq \frac{F_{1}F_{2}}{F_{3}\left( {F_{1} + F_{2}} \right)} \leq 0.6} & (1)\end{matrix}$

The number of frame periods in the transition period may be an evennumber of 2 or greater.

Provided that F₁ represents the first frame frequency (unit: Hz), F₂represents the second frame frequency (unit: Hz), and F_(3_1), F_(3_2),. . . , F_(3_2n−1), and F_(3_2n) represent frame frequencies (unit: Hz)in the transition period in the order from a first driving period sideto a second driving period side, the frame frequencies may satisfy thefollowing formula (2).

[Math.  2] $\begin{matrix}{0.4 \leq \frac{\Sigma_{1}^{n}\left( {\frac{1}{F_{3\_ 2n}} - \frac{1}{F_{{3\_ 2n} - 1}}} \right)}{\frac{1}{F_{2}} - \frac{1}{F_{1}}} \leq 0.6} & (2)\end{matrix}$

In the formula (2), n is an integer of 1 or greater.

The number of frame periods in the transition period may be an oddnumber of 3 or greater.

Provided that F₁ represents the first frame frequency (unit: Hz), F₂represents the second frame frequency (unit: Hz), and F_(3_1), F_(3_2),. . . , F_(3_2n), and F_(3_2n+1) represent frame frequencies (unit: Hz)in the transition period in the order from a first driving period sideto a second driving period side, the frame frequencies may satisfy thefollowing formula (3).

[Math.  3] $\begin{matrix}{0.4 \leq \frac{\frac{1}{F_{3\_ 1}} + {\Sigma_{1}^{n}\left( {\frac{1}{F_{{3\_ 2n} + 1}} - \frac{1}{F_{3\_ 2n}}} \right)}}{\frac{1}{F_{2}} + \frac{1}{F_{1}}} \leq 0.6} & (3)\end{matrix}$

In the formula (3), n is an integer of 1 or greater.

The first frame frequency or the second frame frequency, having a lowerframe frequency, may have a frame frequency of 10 Hz or lower.

The display part may further include a thin film transistor element, andthe thin film transistor element may include a semiconductor layerincluding an oxide semiconductor.

The display device may be a liquid crystal display device.

Advantageous Effects of Invention

The present invention can provide a display device that can change theframe frequency with reduced flickers.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the structure of a display device ofan embodiment.

FIG. 2 is a schematic cross-sectional view of Structure Example 1 of apixel in FIG. 1.

FIG. 3 is a schematic view of an equivalent circuit for simulation inStructure Example 1.

FIG. 4 is a schematic cross-sectional view of Structure Example 2 of apixel in FIG. 1.

FIG. 5 is a schematic view of an equivalent circuit for simulation inStructure Example 2.

FIG. 6 is a schematic cross-sectional view of Structure Example 3 of apixel in FIG. 1.

FIG. 7 is a schematic view of an equivalent circuit for simulation inStructure Example 3.

FIG. 8 is a schematic cross-sectional view of Structure Example 4 of apixel in FIG. 1.

FIG. 9 is a schematic view of an equivalent circuit for simulation inStructure Example 4.

FIG. 10 is a schematic view showing an example of a waveform of an imagesignal for driving in the display device of the embodiment.

FIG. 11 is a graph showing an example of voltage applied to a liquidcrystal layer.

FIG. 12 is a schematic view of a waveform of an image signal for drivingin Classification Example 1.

FIG. 13 is a schematic view of a waveform of an image signal for drivingin Classification Example 2.

FIG. 14 is a schematic view of a waveform of an image signal for drivingin Classification Example 3.

FIG. 15 is a schematic view of a waveform of an image signal for drivingin a display device of Example 1.

FIG. 16 is a schematic view of a waveform of an image signal for drivingin a display device of Example 2.

FIG. 17 is a schematic view of a waveform of an image signal for drivingin a display device of Example 8.

FIG. 18 is a schematic view of a waveform of an image signal for drivingin a display device of Comparative Example 1.

FIG. 19 is a schematic view of a waveform of an image signal for drivingin a display device of Comparative Example 2.

FIG. 20 is a graph showing the results of simulation for the displaydevice of Example 1.

FIG. 21 is a graph showing the results of simulation for the displaydevice of Example 2.

FIG. 22 is a graph showing the results of simulation for a displaydevice of Example 3.

FIG. 23 is a graph showing the results of simulation for a displaydevice of Example 4.

FIG. 24 is a graph showing the results of simulation for a displaydevice of Example 5.

FIG. 25 is a graph showing the results of simulation for a displaydevice of Example 6.

FIG. 26 is a graph showing the results of simulation for a displaydevice of Example 7.

FIG. 27 is a graph showing the results of simulation for the displaydevice of Comparative Example 1.

FIG. 28 is a graph showing the results of simulation for the displaydevice of Comparative Example 2.

FIG. 29 is an enlarged graph showing a part around the transition periodof the graph showing the results of simulation for the display device ofExample 1.

FIG. 30 is an enlarged graph showing a part around the transition periodof the graph showing the results of simulation for the display device ofExample 8.

FIG. 31 is a graph showing the results of simulation for display devicesof Examples 13 and 53 to 59 and Comparative Examples 1 and 6 to 12.

DESCRIPTION OF EMBODIMENTS

The present invention is described below in more detail based on anembodiment with reference to the drawings. The embodiment, however, isnot intended to limit the scope of the present invention. Theconfigurations employed in the embodiment may appropriately be combinedor modified within the spirit of the present invention.

Embodiment

The following is description of the structure and driving of a displaydevice of an embodiment.

(1) Structure of Display Device

FIG. 1 is a block diagram showing the structure of a display device ofan embodiment. As shown in FIG. 1, a display device 1 includes a displaypart 10, a power generation circuit 20, a display control circuit 30, ascanning line drive circuit 40, and a signal line drive circuit 50.

(Display Part)

The display part 10 includes multiple (number: m) scanning lines GL1 toGLm, multiple (number: n) signal lines SL1 to SLn, and multiple (number:m×n) pixels 11 partitioned by the scanning lines GL1 to GLm and thesignal lines SL1 to SLn.

The pixels 11 each include a thin film transistor element 12, a pixelelectrode 13, and a common electrode 14. The thin film transistorelement 12 includes a gate terminal connected to the correspondingscanning line (e.g., scanning line GLm), a source terminal connected tothe corresponding signal line (e.g., signal line SLn), and a drainterminal connected to the pixel electrode 13. The common electrode 14 isprovided electrically commonly over the multiple (number: m×n) pixels11. Between each pixel electrode 13 and the common electrode 14 isformed a pixel capacitance Cp.

Examples of the material for a semiconductor layer included in the thinfilm transistor element 12 include amorphous silicon, polycrystallinesilicon, and an oxide semiconductor. Among these, an oxide semiconductoris preferred in terms of simultaneously achieving low power consumptionand high-speed driving. The oxide semiconductor can achieve low powerconsumption owing to a small amount of off-leakage current (the amountof leakage current when the thin film transistor element 12 is turnedoff) and can also achieve high-speed driving owing to a large amount ofon current (the amount of current when the thin film transistor element12 is turned on). Examples of the material for the oxide semiconductorinclude a compound including indium, gallium, zinc, and, oxygen and acompound including indium, zinc, and oxygen.

In the case where the display device 1 is a liquid crystal displaydevice, structure examples of the pixels 11 include the following.

Structure Example 1

Structure Example 1 relates to a fringe field switching (FFS) modeliquid crystal display device.

FIG. 2 is a schematic cross-sectional view of Structure Example 1 of apixel in FIG. 1. In Structure Example 1, as shown in FIG. 2, a firstsubstrate 60 a, a first alignment film 61, a liquid crystal layer 62, asecond alignment film 63, and a second substrate 64 a are disposed inthe stated order.

The first substrate 60 a includes a first supporting substrate 65, thecommon electrode 14 disposed on the liquid crystal layer 62 side surfaceof the first supporting substrate 65, a first insulating film 66covering the common electrode 14, and the pixel electrodes 13 disposedon the liquid crystal layer 62 side surface of the first insulating film66.

Examples of the first supporting substrate 65 include translucentsubstrates such as a glass substrate, a plastic substrate, and a quartzsubstrate. When the liquid crystal display device is a reflective liquidcrystal display device, the first supporting substrate 65 may be asubstrate without translucency such as a metal substrate including astainless steel substrate.

The common electrode 14 may be formed from an organic material or aninorganic material. Examples of the inorganic material include materialswith translucency and conductivity, such as indium tin oxide (ITO) andindium zinc oxide (IZO).

The first insulating film 66 may be an organic insulating film or aninorganic insulating film. Examples of the organic insulating filminclude polyimide films. Examples of the inorganic insulating filminclude silicon nitride films, silicon oxide films, and siliconoxynitride films. The first insulating film 66 may be a single layer ofone kind of insulating film or a stack of multiple kinds of insulatingfilms. The thickness of the first insulating film 66 is about 50 to 1000nm, for example.

The pixel electrodes 13 may be formed from an organic material or aninorganic material. Examples of the inorganic material include materialswith translucency and conductivity, such as indium tin oxide (ITO) andindium zinc oxide (IZO). The pixel electrodes 13 may each be a singlelayer of one kind of electrode or a stack of multiple kinds ofelectrodes.

The first alignment film 61 and the second alignment film 63 may each bean organic alignment film or an inorganic alignment film, and examplesthereof include a rubbing alignment film and a photoalignment film.Examples of the photoalignment film include a photoalignment filmcontaining a cinnamate group, a photoalignment film containingazobenzene, and a photoalignment film containing a cyclobutane ring. Thefirst alignment film 61 and the second alignment film 63 may each be asingle layer of one kind of alignment film or a stack of multiple kindsof alignment films. When a stack of multiple kinds of alignment films isused, the liquid crystal layer 62 side layer (preferably, outermostlayer on the liquid crystal layer 62 side) may mainly function tocontrol the alignment of liquid crystal molecules, and the layer on theside remote from the liquid crystal layer 62 may mainly function tocontrol the electrical characteristics and the mechanical strength. Thethicknesses of the first alignment film 61 and the second alignment film63 are each about 30 to 300 nm, for example. One or both of the firstalignment film 61 and the second alignment film 63 may not be disposed.

The liquid crystal layer 62 may be formed from a positive liquid crystalmaterial having positive anisotropy of dielectric constant or a negativeliquid crystal material having negative anisotropy of dielectricconstant. In the case of low-frequency driving (e.g., frame frequency:20 Hz or lower), a liquid crystal material that suppresses flickers bythe flexoelectric effect is preferred, that is, a negative liquidcrystal material is preferred. Even in the case of low-frequency driving(e.g., frame frequency: 20 Hz or lower), a positive liquid crystalmaterial may also be used by, for example, limiting the range ofgray-scale values (e.g., limiting the range to the side of highgray-scale values only). The thickness of the liquid crystal layer 62 isabout 1 to 10 μm, for example.

The second substrate 64 a includes a second supporting substrate 70, acolor filter 69 disposed on the liquid crystal layer 62 side surface ofthe second supporting substrate 70, a black matrix 68 disposedseparately from the color filter 69 on the liquid crystal layer 62 sidesurface of the second supporting substrate 70, and a second insulatingfilm 67 covering the color filter 69 and the black matrix 68.

Examples of the second supporting substrate 70 include translucentsubstrates such as a glass substrate, a plastic substrate, and a quartzsubstrate.

The color filter 69 may be formed of a single-color color filter layeror multi-color color filter layers. The color filter 69, when formed ofa multi-color color filter layer, may have any color combination, suchas a combination of red, green, and blue, a combination of red, green,blue, and yellow, and a combination of red, green, blue, and white. Thecolor filter 69 may be formed from a material such as apigment-dispersed color resist. The color filter 69 may not be disposed.In this case, the device can provide monochrome display. In a transverseelectric field mode liquid crystal display device (e.g., the FFS modeliquid crystal display device of the present structure example, thelater described in-plane switching (IPS) mode liquid crystal displaydevice), the electrical characteristics of the color filter 69 areimportant as well as the optical characteristics thereof. The colorfilter 69 has a dielectric tangent (tan δ) of preferably 0.05 or lower,more preferably 0.03 or lower, in the range of the frame frequency to beemployed.

The black matrix 68 may be formed from a material such as black resist.In a transverse electric field mode liquid crystal display device (e.g.,the FFS mode liquid crystal display device of the present structureexample, the later described IPS mode liquid crystal display device),the electrical characteristics of the black matrix 68 are important aswell as the light blocking property and dimensional accuracy thereof.The black matrix 68 has a specific resistance of preferably 1×10¹² Ω·cmor more.

The second insulating film 67 may be formed of, for example, an overcoatlayer. The second insulating film 67 may not be disposed. In atransverse electric field mode liquid crystal display device (e.g., theFFS mode liquid crystal display device of the present structure example,the later described IPS mode liquid crystal display device), theelectrical characteristics of the second insulating film 67 areimportant as well as the light blocking property and dimensionalaccuracy thereof. The second insulating film 67 has a specificresistance of preferably 1×10¹³ Ω·cm or more.

In Structure Example 1, voltage applied between the pixel electrodes 13and the common electrode 14 generates transverse electric fields (fringeelectric fields), thereby enabling control of the alignment of liquidcrystal molecules in the liquid crystal layer 62. The structure shown inFIG. 2 may be modified by switching the positions of the pixelelectrodes 13 and the common electrode 14. This structure can alsoachieve an FFS mode liquid crystal display device.

In Structure Example 1, changes with time of potential differencesbetween the respective layers, which are caused by the electric fieldsgenerated between the pixel electrodes 13 and the common electrode 14,can be simulated in an equivalent circuit as shown in FIG. 3. FIG. 3 isa schematic view of an equivalent circuit for simulation in StructureExample 1. As shown in FIG. 3, the equivalent circuit for StructureExample 1 includes the following circuits A1 to A3 arranged in parallel.

Circuit A1: a circuit for an electric field (electric field EA₁ in FIG.2) passing through the first alignment film 61, the liquid crystal layer62, the first alignment film 61, and the first insulating film 66 in thestated order or in the reverse order

Circuit A2: a circuit for an electric field (electric field EA₂ in FIG.2) passing through the first alignment film 61 and the first insulatingfilm 66 in the stated order or in the reverse order

Circuit A3: a circuit for an electric field (electric field EA₃ in FIG.2) passing through the first insulating film 66

In the circuit corresponding to the first alignment film 61, acapacitance C₆₁ of the first alignment film 61 and a resistance R₆₁ ofthe first alignment film 61 are arranged in parallel. In the circuitcorresponding to the liquid crystal layer 62, a capacitance C₆₂ of theliquid crystal layer 62 and a resistance R₆₂ of the liquid crystal layer62 are arranged in parallel. In the circuit corresponding to the firstinsulating film 66, a capacitance C₆₆ of the first insulating film 66and a resistance R₆₆ of the first insulating film 66 are arranged inparallel. FIG. 3 shows a state where the thin film transistor element 12is turned off.

Structure Example 2

Structure Example 2 relates to an IPS mode liquid crystal displaydevice. Structure Example 2 is the same as Structure Example 1 exceptfor the first substrate. Duplicate explanations thus will beappropriately omitted.

FIG. 4 is a schematic cross-sectional view of Structure Example 2 of apixel in FIG. 1. In Structure Example 2, as shown in FIG. 4, a firstsubstrate 60 b, the first alignment film 61, the liquid crystal layer62, the second alignment film 63, and the second substrate 64 a aredisposed in the stated order.

The first substrate 60 b includes the first supporting substrate 65, thepixel electrodes 13 disposed on the liquid crystal layer 62 side surfaceof the first supporting substrate 65, and the common electrode 14disposed separately from the pixel electrodes 13 on the liquid crystallayer 62 side surface of the first supporting substrate 65.

In Structure Example 2, voltage applied between the pixel electrodes 13and the common electrode 14 generates transverse electric fields,thereby enabling control of the alignment of liquid crystal molecules inthe liquid crystal layer 62.

In Structure Example 2, changes with time of potential differencesbetween the respective layers, which are caused by the electric fieldsgenerated between the pixel electrodes 13 and the common electrode 14,can be simulated by an equivalent circuit as shown in FIG. 5. FIG. 5 isa schematic view of an equivalent circuit for simulation in StructureExample 2. As shown in FIG. 5, the equivalent circuit for StructureExample 2 includes the following circuits B1 to B3 arranged in parallel.

Circuit B1: a circuit for an electric field (electric field EB₁ in FIG.4) passing through the first alignment film 61, the liquid crystal layer62, and the first alignment film 61 in the stated order or in thereverse order

Circuit B2: a circuit for an electric field (electric field EB₂ in FIG.4) passing through the first alignment film 61

Circuit B3: a circuit for an electric field (electric field EB₃ in FIG.4) passing through the first supporting substrate 65

In the circuit corresponding to the first supporting substrate 65, acapacitance C₆₅ of the first supporting substrate 65 and a resistanceR₆₅ of the first supporting substrate 65 are arranged in parallel.

Structure Example 3

Structure Example 3 relates to an IPS mode liquid crystal displaydevice. Structure Example 3 is the same as Structure Example 2 exceptfor the first substrate. Duplicate explanations thus will beappropriately omitted.

FIG. 6 is a schematic cross-sectional view of Structure Example 3 of apixel in FIG. 1. In Structure Example 3, as shown in FIG. 6, a firstsubstrate 60 c, the first alignment film 61, the liquid crystal layer62, the second alignment film 63, and the second substrate 64 a aredisposed in the stated order.

The first substrate 60 c includes the first supporting substrate 65, thepixel electrodes 13 disposed on the liquid crystal layer 62 side surfaceof the first supporting substrate 65, the first insulating film 66covering the pixel electrodes 13, and the common electrode 14 disposedon the liquid crystal layer 62 side surface of the first insulating film66.

In Structure Example 3, voltage applied between the pixel electrodes 13and the common electrode 14 generates transverse electric fields,thereby enabling control of the alignment of liquid crystal molecules inthe liquid crystal layer 62.

In Structure Example 3, changes with time of potential differencesbetween the respective layers, which are caused by the electric fieldsgenerated between the pixel electrodes 13 and the common electrode 14,can be simulated by an equivalent circuit as shown in FIG. 7. FIG. 7 isa schematic view of an equivalent circuit for simulation in StructureExample 3. As shown in FIG. 7, the equivalent circuit for StructureExample 3 includes the following circuits C1 to C4 arranged in parallel.

Circuit C1: a circuit for an electric field (electric field EC₁ in FIG.6) passing through the first insulating film 66, the first alignmentfilm 61, the liquid crystal layer 62, and the first alignment film 61 inthe stated order or in the reverse order

Circuit C2: a circuit for an electric field (electric field EC₂ in FIG.6) passing through the first insulating film 66 and the first alignmentfilm 61 in the stated order or in the reverse order

Circuit C3: a circuit for an electric field (electric field EC₃ in FIG.6) passing through the first insulating film 66

Circuit C4: a circuit for an electric field (electric field EC₄ in FIG.6) passing through the first supporting substrate 65 and the firstinsulating film 66 in the stated order or in the reverse order

Structure Example 4

Structure Example 4 relates to a twisted nematic (TN) mode liquidcrystal display device and a vertical alignment (VA) mode liquid crystaldisplay device. Structure Example 4 is the same as Structure Example 1except for the first substrate and the second substrate. Duplicateexplanations thus will be appropriately omitted.

FIG. 8 is a schematic cross-sectional view of Structure Example 4 of apixel in FIG. 1. In Structure Example 4, as shown in FIG. 8, a firstsubstrate 60 d, the first alignment film 61, the liquid crystal layer62, the second alignment film 63, and a second substrate 64 b aredisposed in the stated order. One of the first alignment film 61 and thesecond alignment film 63 may not be disposed.

The first substrate 60 d includes the first supporting substrate 65 andthe pixel electrodes 13 disposed on the liquid crystal layer 62 sidesurface of the first supporting substrate 65.

The second substrate 64 b includes the second supporting substrate 70,the color filter 69 disposed on the liquid crystal layer 62 side surfaceof the second supporting substrate 70, the black matrix 68 disposedseparately from the color filter 69 on the liquid crystal layer 62 sidesurface of the second supporting substrate 70, and the common electrode14 covering the color filter 69 and the black matrix 68.

In Structure Example 4, voltage applied between the pixel electrodes 13and the common electrode 14 generates a vertical electric field, therebyenabling control of the alignment of liquid crystal molecules in theliquid crystal layer 62.

In Structure Example 4, changes with time of potential differencesbetween the respective layers, which are caused by the electric fieldgenerated between the pixel electrodes 13 and the common electrode 14,can be simulated by an equivalent circuit as shown in FIG. 9. FIG. 9 isa schematic view of an equivalent circuit for simulation in StructureExample 4. As shown in FIG. 9, the equivalent circuit for StructureExample 4 includes the following circuits D1 and D2 arranged inparallel.

Circuit D1: a circuit for an electric field (electric field ED₁ in FIG.8) passing through the first alignment film 61, the liquid crystal layer62, and the second alignment film 63 in the stated order or in thereverse order

Circuit D2: a circuit corresponding to a storage capacitance Cs

In the circuit corresponding to the second alignment film 63, acapacitance C₆₃ of the second alignment film 63 and a resistance R₆₃ ofthe second alignment film 63 are arranged in parallel. In the circuitcorresponding to the storage capacitance Cs, the storage capacitance Cs(capacitance due to an insulating film between the pixel electrodes 13and the gate electrode (e.g., gate insulator, interlayer insulatingfilm)) and a resistance Rs are arranged in parallel.

(Power Generation Circuit)

The power generation circuit 20 generates voltage based on input powersource supplied from the outside (in FIG. 1, the system control unit 2)and supplies the voltage to the display control circuit 30.

(Display Control Circuit)

The display control circuit 30 constitutes the display control part ofthe display device 1. First, the display control circuit 30 generates ascanning line control signal GCT, a signal line control signal SCT, anda common voltage Vcom, based on image signals and control signals inputfrom the outside (in FIG. 1, the system control unit 2). The displaycontrol circuit 30 then outputs the scanning line control signal GCT tothe scanning line drive circuit 40, the signal line control signal SCTto the signal line drive circuit 50, and the common voltage Vcom to thecommon electrode 14.

(Scanning Line Drive Circuit)

The scanning line drive circuit 40 constitutes the driving part of thedisplay device 1. The scanning line drive circuit 40 generates ascanning signal based on the scanning line control signal GCT andoutputs the scanning signal to the scanning lines GL1 to GLm. Thescanning signal allows the scanning line drive circuit 40 tosequentially select and scan the scanning lines GL1 to GLm.

(Signal Line Drive Circuit)

The signal line drive circuit 50 constitutes the driving part of thedisplay device 1. The signal line drive circuit 50 generates an imagesignal for driving based on the signal line control signal SCT andoutputs the image signal for driving to the signal lines SL1 to SLn. Asa result, for example, when the scanning line GLm is selected by thescanning line drive circuit 40, the image signal for driving is inputinto the respective pixels 11 corresponding to the scanning line GLmthrough the signal lines SL1 to SLn.

(2) Driving of Display Device

FIG. 10 is a schematic view showing an example of a waveform of an imagesignal for driving in the display device of the embodiment. Although theamplitude of an image signal for driving usually changes in accordancewith the change of gray scale values, FIG. 10 shows a state without thechange of the gray scale values, where only the frequency of the imagesignal for driving changes, for convenience. The following descriptionalso appropriately refers to FIGS. 1 to 9.

The display control circuit 30 performs control for AC drive of thedisplay part 10, with a voltage applied to the common electrode 14defined as a reference. The term “AC drive” as used herein meansalternate driving between a positive voltage and a negative voltage witha voltage applied to the common electrode 14 defined as a reference. Theterm “positive” as used herein means polarity of a voltage higher thanthe voltage applied to the common electrode 14. The term “negative” asused herein means polarity of a voltage lower than the voltage appliedto the common electrode 14. FIG. 10 shows the polarities of drivingvoltage with the voltage applied to the common electrode 14 defined as areference, and “+” represents positive and “−” represents negative (thesame shall apply to the other drawings).

The method for AC drive is not particularly limited. Examples thereofinclude a frame inversion method in which the polarities of all thepixels are inverted to the same polarity at once for each frame, a lineinversion method in which the polarities of pixels in adjacent rows areinverted to opposite polarities for each frame, a column inversionmethod in which the polarities of pixels in adjacent columns areinverted to opposite polarities for each frame, a dot inversion methodin which the polarities of adjacent pixels are inverted to oppositepolarities for each frame, and a method in which the polarities of twoadjacent units each including a plurality of pixels in the row directionor in the column direction are inverted to opposite polarities for eachframe.

The display control circuit 30 provides a transition period between afirst driving period and a second driving period in switching from thefirst driving period to the second driving period (e.g., switchingbetween a moving image and a still image). The first driving periodallows the display part 10 to be driven at a first frame frequency F₁.The second driving period allows the display part 10 to be driven at asecond frame frequency F₂ different from the first frame frequency F₁.The transition period includes a period where the display part 10 isdriven at at least one frame frequency with a value between the firstframe frequency F₁ and the second frame frequency F₂. Here, the phrase“a value between X and Y” as used herein means “a value higher than Xand lower than Y” (in the case of X<Y), or “a value higher than Y andlower than X” (in the case of Y<X).

FIG. 10 includes, as a transition period, a period where the displaypart 10 is driven at a frame frequency F₃, where F₂<F₃<F₁. Thetransition period includes, with the voltage applied to the commonelectrode 14 defined as a reference, a positive period where the displaypart 10 is driven at a positive voltage and a negative period where thedisplay part 10 is driven at a negative voltage. The positive period inthe transition period includes one frame period (length (time): T_(p1)).The negative period in the transition period includes two frame periods(length (time): T_(n1), T_(n2)). In the transition period, provided thatT_(p) represents the total duration of the positive period and T_(n)represents the total duration of the negative period, T_(p) and T_(n)are expressed by the following formulas (a) and (b). T_(p) and T_(n)have different values (T_(p)<T_(n)).

T _(p) =T _(p1)  (a)

T _(n) =T _(n1) +T _(n2)  (b)

When there is a difference between the total duration of the positiveperiod T_(p) and the total duration of the negative period T_(n) in thetransition period as in the present embodiment, Vcom shift whenswitching from the first frame frequency F₁ (first driving period) tothe second frame frequency F₂ (second driving period) can be suppressed.This results in suppression of flickers. For example, when the displaydevice 1 is a liquid crystal display device, suppression of variation ineffective voltage applied to the liquid crystal layer 62 enablessuppression of Vcom shift. The phrase “effective voltage applied to theliquid crystal layer” is also referred to as “a DC voltage componentapplied to the liquid crystal layer”. The phrase “a DC voltage componentapplied to the liquid crystal layer” means a DC voltage V_(DC_LC)corresponding to a reference voltage applied to the liquid crystallayer, at which, as schematically shown in FIG. 11, the area of thepositive frame period and the area of the negative frame period areequal to each other. FIG. 11 is a graph showing an example of voltageapplied to the liquid crystal layer.

Although the first frame frequency F₁, the second frame frequency F₂,and the frame frequency F₃ in the transition period satisfy the relationof: F₂<F₃<F₁ (switching from a high frequency (F₁) to a low frequency(F₂)) in FIG. 10, they may satisfy the relation of: F₁<F₃<F₂ (switchingfrom a low frequency (F₁) to a high frequency (F₂)).

Although the frame frequency in the transition period includes one framefrequency F₃ in FIG. 10, it may include multiple frame frequencies. Inthis case, at least one of the multiple frame frequencies may have avalue between the first frame frequency F₁ and the second framefrequency F₂.

In the present embodiment, the term “frame period” means a period fromdriving at a voltage with a certain polarity (e.g., writing a voltagewith a certain polarity) to driving at a voltage with the counterpolarity thereof (e.g., writing a voltage with the counter polaritythereof), and the term “frame frequency” means the reciprocal number ofthe length (time) of the period. The term “driving” as used hereinincludes at least driving for refreshing the screen of the display part10 and may also include driving for pausing in refreshing the screen ofthe display part 10. A period for refreshing the screen of the displaypart 10 is referred to as a “refreshing period”, and a period forpausing in refreshing the screen of the display part 10 is referred toas a “pause period”. The frame period may include refreshing period(s)only or may include refreshing period(s) and pause period(s).

In the refreshing period, the signal line drive circuit 50 outputs animage signal for driving to the signal lines SL1 to SLn, and thescanning line drive circuit 40 sequentially selects and scans thescanning lines GL1 to GLm with a scanning signal. When the scanning lineGLm is selected, for example, each thin film transistor element 12corresponding to the scanning line GLm is turned on, and then a voltagefor an image signal for driving is written to the corresponding pixel 11(pixel capacitance Cp). Thereby, the screen of the display part 10 isrefreshed. Then, when the display device 1 is a liquid crystal displaydevice, for example, the thin film transistor element 12 is turned off.Here, the written voltage may be regarded as being practically helduntil the next refreshment of the screen of the display part 10 as longas the off-leakage current of the thin film transistor element 12 islow, the leakage currents of members such as the liquid crystal layer,the alignment film, and the insulating film are low, and the RC timeconstants of members such as the liquid crystal layer, the alignmentfilm, and the insulating film are balanced.

In the pause period, one or both of the scanning line drive circuit 40and the signal line drive circuit 50 pauses. For example, the scanningline drive circuit 40 pauses when output of the scanning line controlsignal GCT to the scanning line drive circuit 40 stops or the scanningline control signal GCT has a fixed potential. Similarly, the signalline drive circuit 50 pauses when output of the signal line controlsignal SCT to the signal line drive circuit 50 stops or the signal linecontrol signal SCT has a fixed potential. As a result, the scanninglines GL1 to GLm are not scanned and no image signal for driving iswritten to the pixels 11 (pixel capacitances Cp). However, as describedabove, in the pause period, the voltage having been written in therefreshing period immediately before the pause period (specifically, thelast frame period in the refreshing period immediately before the pauseperiod) is held. Thus, the image on the screen refreshed in therefreshing period immediately before the pause period (specifically, thelast frame period in the refreshing period immediately before the pauseperiod) is kept displayed. Since one or both of the scanning line drivecircuit 40 and the signal line drive circuit 50 pauses in the pauseperiod, low power consumption can be achieved.

Driving for pausing in refreshing the screen of the display part 10after refreshing the screen of the display part 10 is also referred toas “pause driving”. When pause driving is performed in a transitionperiod, the total duration of positive period T_(p) and the totalduration of negative period T_(n) each correspond to the total durationof the refreshing period(s) and the pause period(s). Although a waveformof an image signal for driving does not need to be one representing animage signal in a pause period when pause driving is performed, FIG. 10shows a simple square wave for convenience.

At least one period selected from the group consisting of the firstdriving period, the second driving period, and the transition period mayinclude a frame period including a refreshing period and a pause periodthat is longer than the refreshing period. Such pause driving canachieve lower power consumption than driving that performs refreshmentonly.

The transition period may include refreshing period(s) only or mayinclude refreshing period(s) and pause period(s).

One frame period may include one or more refreshing periods. Forexample, when the length (time) of a frame period is one second (framefrequency: 1 Hz), a positive (negative) voltage may be written only onceor multiple times during the one second.

Although the present embodiment gives an example in which switching isperformed between two frame frequencies (switching from the first framefrequency F₁ to the second frame frequency F₂) as shown in FIG. 10,stepwise switching between three or more different frame frequencies isalso allowable. This case includes multiple processes for changing theframe frequency. At least one of these processes may include atransition period.

Preferably, there is a difference between the polarity of the positiveperiod or the negative period in the transition period, whichever has alonger total duration, and the polarity of a frame period that belongsto the first driving period or the second driving period, whichever hasa lower frame frequency, and is closest to the transition period.Thereby, Vcom shift is more suppressed when switching from the firstframe frequency F₁ (first driving period) to the second frame frequencyF₂ (second driving period). This results in better suppression offlickers. A specific example having such a feature is shown in FIG. 10,which can be described as follows.

(A) One of the positive period and the negative period in the transitionperiod, having a longer total duration, is the negative period(T_(p)<T_(n)) and the polarity thereof is negative.

(B) One of the first driving period and the second driving period,having a lower frame frequency, is the second driving period (F₂<F₁). Inthe second driving period, the polarity of a frame period closest to thetransition period is positive.

Accordingly, the polarity of (A) and the polarity of (B) are differentfrom each other.

Preferred relations of the frame frequencies between the first drivingperiod, the second driving period, and the transition period aredescribed based on the following classification examples.

Classification Example 1

Classification Example 1 relates to the case where the number of frameperiods in the transition period is 1.

FIG. 12 is a schematic view of a waveform of an image signal for drivingin Classification Example 1. FIG. 12 includes the first driving period(first frame frequency F₁ (unit: Hz), the length (time) T₁ (unit:second) of the frame period), the second driving period (second framefrequency F₂ (unit: Hz), the length (time) T₂ (unit: second) of theframe period), and the transition period (frame frequency F₃ (unit: Hz),the length (time) T₃ (unit: second) of the frame period) between thefirst driving period and the second driving period.

The frame frequencies preferably satisfy a relation represented by thefollowing formula (1). In this case, Vcom shift is more suppressed whenswitching from the first frame frequency F₁ (first driving period) tothe second frame frequency F₂ (second driving period). This results inbetter suppression of flickers.

[Math.  4] $\begin{matrix}{0.4 \leq \frac{F_{1}F_{2}}{F_{3}\left( {F_{1} + F_{2}} \right)} \leq 0.6} & (1)\end{matrix}$

The frame frequencies particularly preferably satisfy a relationrepresented by the following formula (1-1).

[Math.  5] $\begin{matrix}{\frac{F_{1}F_{2}}{F_{3}\left( {F_{1} + F_{2}} \right)} = 0.5} & \left( {1\text{-}1} \right)\end{matrix}$

Classification Example 2

Classification Example 2 relates to the case where the number of frameperiods in the transition period is an even number of 2 or greater.

FIG. 13 is a schematic view of a waveform of an image signal for drivingin Classification Example 2. FIG. 13 includes the first driving period(first frame frequency F₁ (unit: Hz), the length (time) T₁ (unit:second) of the frame period), the second driving period (second framefrequency F₂ (unit: Hz), the length (time) T₂ (unit: second) of theframe period), and the transition period (frame frequencies F_(3_1),F_(3_2), . . . , F_(3_2n−1), and F_(3_2n) (unit: Hz), the lengths (time)T_(3_1), T_(3_2), . . . , T_(3_2n−1), and T_(3_2n) (unit: second) of theframe periods) between the first driving period and the second drivingperiod.

The frame frequencies preferably satisfy a relation represented by thefollowing formula (2). In this case, Vcom shift is more suppressed whenswitching from the first frame frequency F₁ (first driving period) tothe second frame frequency F₂ (second driving period). This results inbetter suppression of flickers.

[Math.  6] $\begin{matrix}{0.4 \leq \frac{\Sigma_{1}^{n}\left( {\frac{1}{F_{3\_ 2n}} - \frac{1}{F_{{3\_ 2n} - 1}}} \right)}{\frac{1}{F_{2}} - \frac{1}{F_{1}}} \leq 0.6} & (2)\end{matrix}$

In the formula (2), n is an integer of 1 or greater.

The frame frequencies particularly preferably satisfy a relationrepresented by the following formula (2-1).

[Math.  7] $\begin{matrix}{\frac{\Sigma_{1}^{n}\left( {\frac{1}{F_{3\_ 2n}} - \frac{1}{F_{{3\_ 2n} - 1}}} \right)}{\frac{1}{F_{2}} - \frac{1}{F_{1}}} = 0.5} & \left( {2\text{-}1} \right)\end{matrix}$

In the formula (2-1), n is an integer of 1 or greater.

Classification Example 3

Classification Example 3 relates to the case where the number of frameperiods in the transition period is an odd number of 3 or greater.

FIG. 14 is a schematic view of a waveform of an image signal for drivingin Classification Example 3. FIG. 14 includes the first driving period(first frame frequency F₁ (unit: Hz), the length (time) T₁ (unit:second) of the frame period), the second driving period (second framefrequency F₂ (unit: Hz), the length (time) T₂ (unit: second) of theframe period), and the transition period (frame frequencies F_(3_1),F_(3_2), . . . , F_(3_2n), and F_(3_2n+1) (unit: Hz), the lengths (time)T_(3_1), T_(3_2), . . . , T_(3_2n), and T_(3_2n+1) (unit: second) of theframe periods) between the first driving period and the second drivingperiod.

The frame frequencies preferably satisfy a relation represented by thefollowing formula (3). In this case, Vcom shift is more suppressed whenswitching from the first frame frequency F₁ (first driving period) tothe second frame frequency F₂ (second driving period). This results inbetter suppression of flickers.

[Math.  8] $\begin{matrix}{0.4 \leq \frac{\frac{1}{F_{3\_ 1}} + {\Sigma_{1}^{n}\left( {\frac{1}{F_{{3\_ 2n} + 1}} - \frac{1}{F_{3\_ 2n}}} \right)}}{\frac{1}{F_{2}} + \frac{1}{F_{1}}} \leq 0.6} & (3)\end{matrix}$

In the formula (3), n is an integer of 1 or greater.

The frame frequencies particularly preferably satisfy a relationrepresented by the following formula (3-1).

[Math.  9] $\begin{matrix}{\frac{\frac{1}{F_{3\_ 1}} + {\Sigma_{1}^{n}\left( {\frac{1}{F_{{3\_ 2n} + 1}} - \frac{1}{F_{3\_ 2n}}} \right)}}{\frac{1}{F_{2}} + \frac{1}{F_{1}}} = 0.5} & \left( {3\text{-}1} \right)\end{matrix}$

In the formula (3-1), n is an integer of 1 or greater.

The first frame frequency F₁ or the second frame frequency F₂, having alower frame frequency, may have a frame frequency of 10 Hz or lower. Inthe case of driving without a transition period differently from thepresent embodiment, the influence of Vcom shift is greater when thelower of the first frame frequency F₁ and the second frame frequency F₂is 10 Hz or lower. In contrast, in the present embodiment, even when thelower of the first frame frequency F₁ and the second frame frequency F₂is 10 Hz or lower, Vcom shift is effectively suppressed.

The display device 1 is not limited and may be, for example, a displaydevice which performs driving such as low-frequency driving and pausedriving to achieve low power consumption and maintain display qualitysimultaneously and in which the voltage changes with time according tothe balance of the RC time constants between the multiple materials. Thedisplay device 1 is preferably a liquid crystal display device.

When the display device 1 is a liquid crystal display device, thepresent embodiment can exert the effects thereof in a liquid crystaldisplay device of any display mode (e.g., FFS mode, IPS mode, TN mode,and VA mode as shown in Structure Examples 1 to 4). Especially bettereffects are exerted in an FFS mode liquid crystal display device(Structure Example 1) and an IPS mode liquid crystal display device(Structure Example 3: a structure in which the pixel electrodes 13 andthe common electrode 14 are not disposed in the same layer). In thesedevices, the balance of the RC time constants between the firstalignment film 61, the second alignment film 63, the liquid crystallayer 62, and the first insulating film 66 (insulating film between thepixel electrodes 13 and the common electrode 14) is important. In aliquid crystal display device of such a display mode, a remarkableeffect is exerted when the RC time constants are significantly differentbetween the first alignment film 61, the second alignment film 63, theliquid crystal layer 62, and the first insulating film 66. In a liquidcrystal display device of such a display mode, the first alignment film61 and the second alignment film 63 each have a specific resistance ofabout 1×10¹² to 5×10¹⁶ Ω·cm, the liquid crystal layer 62 has a specificresistance of about 1×10¹¹ to 1×10¹⁶ Ω·cm, and the first insulating film66 has a specific resistance of about 1×10¹³ to 5×10¹⁶ Ω·cm. Aparticularly remarkable effect is exerted when the first alignment film61 and the second alignment film 63 each have a specific resistance of1×10¹⁵ Ω·cm or more and the liquid crystal layer 62 has a specificresistance of 1×10¹⁴ Ω·cm or less. The effect may be exerted in any caseof transmissive and reflective liquid crystal display devices.

EXAMPLES AND COMPARATIVE EXAMPLES

The present invention is described below in more detail based onexamples and comparative examples. The examples, however, are notintended to limit the scope of the present invention.

A display device of each of the examples and comparative examples wasassumed to be an FFS mode liquid crystal display device (StructureExample 1) as shown in FIG. 2 and FIG. 3, and simulation was performedfor one pixel thereof. The conditions for the simulation were asfollows.

(Alignment Film)

The first alignment film 61 and the second alignment film 63 each had aspecific resistance of 1×10¹⁵ Ω·cm, a dielectric constant of 3.9, and athickness of 100 nm.

(Liquid Crystal Layer)

The liquid crystal layer 62 had a specific resistance of 1×10¹³ Ω·cm, adielectric constant of 6.0, and a thickness of 3.3 μm.

(Insulating Film)

The first insulating film 66 had a specific resistance of 1×10¹⁵ Ω·cm, adielectric constant of 6.5, and a thickness of 200 nm.

Examples 1 to 59 and Comparative Examples 1 to 12

An image signal for driving of the display device of each of theexamples and comparative examples was made to have a configuration asshown in Tables 1 to 12. In each table, “polarity” indicates thepolarity of a frame period where driving is performed at thecorresponding frame frequency. In particular, “polarity <final>”indicates the polarity of the final frame period in the driving period,and “polarity <initial>” indicates the polarity of the first frameperiod in the driving period. The frame frequencies in the transitionperiod are expressed as F_(3_1), F_(3_2) . . . in the order from thefirst driving period side to the second driving period side.

Among Examples 1 to 59 and Comparative Examples 1 to 12, waveforms of animage signal for driving in Examples 1, 2, and 8, and ComparativeExamples 1 and 2 are shown in FIGS. 15 to 19 as representative examples.FIG. 15 is a schematic view of a waveform of an image signal for drivingin the display device of Example 1. FIG. 16 is a schematic view of awaveform of an image signal for driving in the display device of Example2. FIG. 17 is a schematic view of a waveform of an image signal fordriving in the display device of Example 8. FIG. 18 is a schematic viewof a waveform of an image signal for driving in the display device ofComparative Example 1. FIG. 19 is a schematic view of a waveform of animage signal for driving in the display device of Comparative Example 2.

In Examples 1 to 59 and Comparative Examples 1 to 12, when the framefrequency was 60 Hz or higher, each frame period included refreshingperiod(s) only. Meanwhile, when the frame frequency is lower than 60 Hz,each frame period included refreshing period(s) and pause period(s).Additionally, in Examples 1 to 59, there was a difference between thepolarity of the positive period or the negative period in the transitionperiod, whichever had a longer total duration (e.g., in Example 1,negative period: the polarity was negative), and the polarity of a frameperiod that belonged to the first driving period or the second drivingperiod, whichever had a lower frame frequency, and was closest to thetransition period (e.g., in Example 1, the first frame period in thesecond driving period: the polarity was positive).

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6First driving F₁ (Hz) 60 60 120 60 60 60 period Polarity <final>Positive Negative Negative Negative Negative Negative Transition F₃ _(—)₁ (Hz) 2 30 5 20 30 90 period Polarity Negative Positive PositivePositive Positive Positive F₃ _(—) ₂ (Hz) 2 1 40 30 30 90 PolarityPositive Negative Negative Negative Negative Negative F₃ _(—) ₃ (Hz) 2 —3 1 1 2 Polarity Negative — Positive Positive Positive Positive F₃ _(—)₄ (Hz) — — — — — — Polarity — — — — — — Total duration of 0.500 0.0330.533 1.050 1.033 0.511 positive period (sec) Total duration of 1.0001.000 0.025 0.033 0.033 0.011 negative period (sec) Second driving F₂(Hz) 1 0.5 1 0.5 0.5 1 period Polarity <initial> Positive PositiveNegative Negative Negative Negative

TABLE 2 Example 7 Example 8 Example 9 Example 10 Example 11 Example 12First driving F₁ (Hz) 2 60 60 60 60 60 period Polarity <final> PositivePositive Negative Negative Negative Negative Transition F₃ _(—) ₁ (Hz) 52 9.8 4.9 3.3 2.5 period Polarity Negative Negative Positive PositivePositive Positive F₃ _(—) ₂ (Hz) 10 — — — — — Polarity Positive — — — —— F₃ _(—) ₃ (Hz) 6 — — — — — Polarity Negative — — — — — F₃ _(—) ₄ (Hz)— — — — — — Polarity — — — — — — Total duration of 0.100 0 0.102 0.2040.303 0.400 positive period (sec) Total duration of 0.367 0.500 0 0 0 0negative period (sec) Second driving F₂ (Hz) 30 1 1 1 1 1 periodPolarity <initial> Positive Positive Negative Negative Negative Negative

TABLE 3 Example 13 Example 14 Example 15 Example 16 Example 17 Example18 First driving F₁ (Hz) 60 60 60 60 60 10 period Polarity <final>Negative Negative Negative Negative Negative Negative Transition F₃ _(—)₁ (Hz) 2 1.6 1.4 1.2 1.1 4.55 period Polarity Positive Positive PositivePositive Positive Positive F₃ _(—) ₂ (Hz) — — — — — — Polarity — — — — —— F₃ _(—) ₃ (Hz) — — — — — — Polarity — — — — — — F₃ _(—) ₄ (Hz) — — — —— — Polarity — — — — — — Total duration of 0.500 0.625 0.714 0.833 0.9090.220 positive period (sec) Total duration of 0 0 0 0 0 0 negativeperiod (sec) Second driving F₂ (Hz) 1 1 1 1 1 1 period Polarity<initial> Negative Negative Negative Negative Negative Negative

TABLE 4 Example 19 Example 20 Example 21 Example 22 Example 23 Example24 First driving F₁ (Hz) 10 10 10 10 10 10 period Polarity <final>Negative Negative Negative Negative Negative Negative Transition F₃ _(—)₁ (Hz) 3.03 2.27 1.82 1.52 1.3 1.14 period Polarity Positive PositivePositive Positive Positive Positive F₃ _(—) ₂ (Hz) — — — — — — Polarity— — — — — — F₃ _(—) ₃ (Hz) — — — — — — Polarity — — — — — — F₃ _(—) ₄(Hz) — — — — — — Polarity — — — — — — Total duration of 0.330 0.4410.549 0.658 0.769 0.877 positive period (sec) Total duration of 0 0 0 00 0 negative period (sec) Second driving F₂ (Hz) 1 1 1 1 1 1 periodPolarity <initial> Negative Negative Negative Negative Negative Negative

TABLE 5 Example 25 Example 26 Example 27 Example 28 Example 29 Example30 First driving F₁ (Hz) 4 4 4 4 4 2 period Polarity <final> NegativeNegative Negative Negative Negative Negative Transition F₃ _(—) ₁ (Hz)2.67 2 1.6 1.34 1.14 1.9 period Polarity Positive Positive PositivePositive Positive Positive F₃ _(—) ₂ (Hz) — — — — — — Polarity — — — — —— F₃ _(—) ₃ (Hz) — — — — — — Polarity — — — — — — F₃ _(—) ₄ (Hz) — — — —— — Polarity — — — — — — Total duration of 0.375 0.500 0.625 0.746 0.8770.526 positive period (sec) Total duration of 0 0 0 0 0 0 negativeperiod (sec) Second driving F₂ (Hz) 1 1 1 1 1 1 period Polarity<initial> Negative Negative Negative Negative Negative Negative

TABLE 6 Example 31 Example 32 Example 33 Example 34 Example 35 Example36 First driving F₁ (Hz) 2 2 2 2 2 2 period Polarity <final> NegativeNegative Negative Negative Negative Negative Transition F₃ _(—) ₁ (Hz)1.67 1.48 1.33 1.21 1.11 1.03 period Polarity Positive Positive PositivePositive Positive Positive F₃ _(—) ₂ (Hz) — — — — — — Polarity — — — — —— F₃ _(—) ₃ (Hz) — — — — — — Polarity — — — — — — F₃ _(—) ₄ (Hz) — — — —— — Polarity — — — — — — Total duration of 0.599 0.676 0.752 0.826 0.9010.971 positive period (sec) Total duration of 0 0 0 0 0 0 negativeperiod (sec) Second driving F₂ (Hz) 1 1 1 1 1 1 period Polarity<initial> Negative Negative Negative Negative Negative Negative

TABLE 7 Example 37 Example 38 Example 39 Example 40 Example 41 Example42 First driving F₁ (Hz) 60 60 60 60 60 60 period Polarity <final>Negative Negative Negative Negative Negative Negative Transition F₃ _(—)₁ (Hz) 20 20 20 20 20 20 period Polarity Positive Positive PositivePositive Positive Positive F₃ _(—) ₂ (Hz) 4 2.9 2.25 1.87 1.57 1.35Polarity Negative Negative Negative Negative Negative Negative F₃ _(—) ₃(Hz) — — — — — — Polarity — — — — — — F₃ _(—) ₄ (Hz) — — — — — —Polarity — — — — — — Total duration of 0.050 0.050 0.050 0.050 0.0500.050 positive period (sec) Total duration of 0.250 0.345 0.444 0.5350.637 0.741 negative period (sec) Second driving F₂ (Hz) 1 1 1 1 1 1period Polarity <initial> Positive Positive Positive Positive PositivePositive

TABLE 8 Example 43 Example 44 Example 45 Example 46 Example 47 Example48 First driving F₁ (Hz) 60 60 60 60 60 60 period Polarity <final>Negative Negative Negative Negative Negative Negative Transition F₃ _(—)₁ (Hz) 20 10 10 45 30 30 period Polarity Positive Positive PositivePositive Positive Positive F₃ _(—) ₂ (Hz) 1.2 2 1.71 30 40 40 PolarityNegative Negative Negative Negative Negative Negative F₃ _(—) ₃ (Hz) — —— 90 5 3.4 Polarity — — — Positive Positive Positive F₃ _(—) ₄ (Hz) — —— 1 — — Polarity — — — Negative — — Total duration of 0.050 0.100 0.1000.033 0.233 0.327 positive period (sec) Total duration of 0.833 0.5000.585 1.033 0.025 0.025 negative period (sec) Second driving F₂ (Hz) 1 11 0.5 1 1 period Polarity <initial> Positive Positive Positive PositiveNegative Negative

TABLE 9 Example 49 Example 50 Example 51 Example 52 Example 53 Example54 First driving F₁ (Hz) 60 60 60 60 60 60 period Polarity <final>Negative Negative Negative Negative Negative Negative Transition F₃ _(—)₁ (Hz) 30 30 30 30 40 24 period Polarity Positive Positive PositivePositive Positive Positive F₃ _(—) ₂ (Hz) 40 40 40 40 — — PolarityNegative Negative Negative Negative — — F₃ _(—) ₃ (Hz) 2.5 2 1.67 1.42 —— Polarity Positive Positive Positive Positive — — F₃ _(—) ₄ (Hz) — — —— — — Polarity — — — — — — Total duration of 0.433 0.533 0.632 0.7380.025 0.042 positive period (sec) Total duration of 0.025 0.025 0.0250.025 0 0 negative period (sec) Second driving F₂ (Hz) 1 1 1 1 30 15period Polarity <initial> Negative Negative Negative Negative NegativeNegative

TABLE 10 Example 55 Example 56 Example 57 Example 58 Example 59 Firstdriving F₁ (Hz) 60 60 60 60 60 period Polarity <final> Negative NegativeNegative Negative Negative Transition F₃ _(—) ₁ (Hz) 17 9.2 7.5 5.7 3.9period Polarity Positive Positive Positive Positive Positive F₃ _(—) ₂(Hz) — — — — — Polarity — — — — — F₃ _(—) ₃ (Hz) — — — — — Polarity — —— — — F₃ _(—) ₄ (Hz) — — — — — Polarity — — — — — Total duration of0.059 0.109 0.133 0.175 0.256 positive period (sec) Total duration of 00 0 0 0 negative period (sec) Second driving F₂ (Hz) 10 5 4 3 2 periodPolarity <initial> Negative Negative Negative Negative Negative

TABLE 11 Comparative Comparative Comparative Comparative ComparativeComparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6First driving F₁ (Hz) 60  60 10  4 2 60  period Polarity <final>Positive Positive Positive Positive Positive Positive Transition F₃ _(—)₁ (Hz) — 2 — — — — period Polarity — Negative — — — — F₃ _(—) ₂ (Hz) — 2— — — — Polarity — Positive — — — — F₃ _(—) ₃ (Hz) — — — — — — Polarity— — — — — — F₃ _(—) ₄ (Hz) — — — — — — Polarity — — — — — — Totalduration of 0 0.500 0 0 0 0 positive period (sec) Total duration of 00.500 0 0 0 0 negative period (sec) Second driving F₂ (Hz) 1 1 1 1 1 30 period Polarity <initial> Negative Negative Negative Negative NegativeNegative

TABLE 12 Comparative Comparative Comparative Comparative ComparativeComparative Example 7 Example 8 Example 9 Example 10 Example 11 Example12 First driving F₁ (Hz) 60  60  60  60  60  60  period Polarity <final>Positive Positive Positive Positive Positive Positive Transition F₃ _(—)₁ (Hz) — — — — — — period Polarity — — — — — — F₃ _(—) ₂ (Hz) — — — — —— Polarity — — — — — — F₃ _(—) ₃ (Hz) — — — — — — Polarity — — — — — —F₃ _(—) ₄ (Hz) — — — — — — Polarity — — — — — — Total duration of 0 0 00 0 0 positive period (sec) Total duration of 0 0 0 0 0 0 negativeperiod (sec) Second driving F₂ (Hz) 15  10  5 4 3 2 period Polarity<initial> Negative Negative Negative Negative Negative Negative

[Evaluation 1]

In the display device of each of Examples 1 to 7 and ComparativeExamples 1 and 2, the DC voltage component V_(DC_LC) applied to theliquid crystal layer was calculated with a SPICE simulator whenswitching from the first frame frequency F₁ (first driving period) tothe second frame frequency F₂ (second driving period) using theaforementioned image signal for driving. FIGS. 20 to 28 show thesimulation results. FIG. 20 is a graph showing the results of simulationfor the display device of Example 1. FIG. 21 is a graph showing theresults of simulation for the display device of Example 2. FIG. 22 is agraph showing the results of simulation for the display device ofExample 3. FIG. 23 is a graph showing the results of simulation for thedisplay device of Example 4. FIG. 24 is a graph showing the results ofsimulation for the display device of Example 5. FIG. 25 is a graphshowing the results of simulation for the display device of Example 6.FIG. 26 is a graph showing the results of simulation for the displaydevice of Example 7. FIG. 27 is a graph showing the results ofsimulation for the display device of Comparative Example 1. FIG. 28 is agraph showing the results of simulation for the display device ofComparative Example 2.

As shown in FIGS. 20 to 26, in Examples 1 to 7, variation in DC voltagecomponent V_(DC_LC) applied to the liquid crystal layer was suppressed(the variation period was short) when changing the frame frequency. Thesuppression of Vcom shift resulted in suppression of flickers. In FIGS.20 to 26, the DC voltage component V_(DC_LC) applied to the liquidcrystal layer seems to momently vary when changing the frame frequency.This is because, according to the definition shown in FIG. 11, the DCvoltage component V_(DC_LC) applied to the liquid crystal layer alwaysvaries before and after changing the frame frequency. This momentaryvariation thus caused no problem for display.

Meanwhile, as shown in FIGS. 27 and 28, in Comparative Examples 1 and 2,the DC voltage component V_(DC_LC) applied to the liquid crystal layersignificantly varied (the variation period was long) when changing theframe frequency. Occurrence of Vcom shift resulted in increasedflickers. The reason for this is that, in Comparative Example 1, notransition period was provided between the first driving period and thesecond driving period, and that, in Comparative Example 2, the totalduration of the positive period and the total duration of the negativeperiod in the transition period were the same as each other.

[Evaluation 2]

In the display device of each of Examples 1 and 8, the DC voltagecomponent V_(DC_LC) applied to the liquid crystal layer was calculatedwith a SPICE simulator when switching from the first frame frequency F₁(first driving period) to the second frame frequency F₂ (second drivingperiod) using the aforementioned image signal for driving. FIGS. 29 and30 show the simulation results. FIG. 29 is an enlarged graph showing apart around the transition period of the graph showing the results ofsimulation for the display device of Example 1. FIG. 30 is an enlargedgraph showing a part around the transition period of the graph showingthe results of simulation for the display device of Example 8. InExamples 1 and 8, the structure of the image signal for driving was thesame as each other except for the number of frame periods in thetransition period (Example 1: 3, Example 8: 1).

As shown in FIGS. 29 and 30, in Example 8, the variation in DC voltagecomponent V_(DC_LC) applied to the liquid crystal layer when changingthe frame frequency was more suppressed as compared with Example 1. Thisshows that the variation is more effectively suppressed when the numberof frame periods in the transition period is 1.

[Evaluation 3]

Evaluation was made for preferred relations of the frame frequenciesbetween the first driving period, the second driving period, and thetransition period in the case where the number of frame periods in thetransition period was 1 (Classification Example 1).

(Evaluation 3-1)

In the display device of each of Examples 9 to 17 and ComparativeExample 1, the variation amount (|ΔV_(DC_LC)|) of the DC voltagecomponent V_(DC_LC) applied to the liquid crystal layer was calculatedwith a SPICE simulator when switching from the first frame frequency F₁(first driving period) to the second frame frequency F₂ (second drivingperiod) using the aforementioned image signal for driving. Table 13shows the simulation results. In Table 13, X indicates values calculatedfrom the following formula (x) (the same shall apply to the othertables). The variation amount (|ΔV_(DC_LC)|) of the DC voltage componentV_(DC_LC) applied to the liquid crystal layer was calculated exceptingthe momentary variation of the DC voltage component V_(DC_LC) applied tothe liquid crystal layer in the part where the frame frequencies wereswitched (the same shall apply to the other simulations).

[Math.  10] $\begin{matrix}{X = \frac{F_{1}F_{2}}{F_{3\_ 1}\left( {F_{1} + F_{2}} \right)}} & (x)\end{matrix}$

TABLE 13 F₁ F₃ _(—) ₁ F₂ |ΔV_(DC) _(—) _(LC)| (Hz) (Hz) (Hz) X (mV)Example 9 60 9.8 1 0.1 41 Example 10 60 4.9 1 0.2 31 Example 11 60 3.3 10.3 21 Example 12 60 2.5 1 0.4 11 Example 13 60 2 1 0.5 0 Example 14 601.6 1 0.6 10 Example 15 60 1.4 1 0.7 20 Example 16 60 1.2 1 0.8 30Example 17 60 1.1 1 0.9 39 Comparative 60 — 1 — 50 Example 1

As shown in Table 13, in Examples 9 to 17, the variation amount(|ΔV_(DC_LC)|) of the DC voltage component V_(DC_LC) applied to theliquid crystal layer when changing the frame frequency was small and theVcom shift was suppressed as compared with Comparative Example 1. Inparticular, Vcom shift was more suppressed in Examples 12 to 14.

(Evaluation 3-2)

In the display device of each of Examples 18 to 24 and ComparativeExample 3, the variation amount (|ΔV_(DC_LC)|) of the DC voltagecomponent V_(DC_LC) applied to the liquid crystal layer was calculatedwith a SPICE simulator when switching from the first frame frequency F₁(first driving period) to the second frame frequency F₂ (second drivingperiod) using the aforementioned image signal for driving. Table 14shows the simulation results.

TABLE 14 F₁ F₃ _(—) ₁ F₂ |ΔV_(DC) _(—) _(LC)| (Hz) (Hz) (Hz) X (mV)Example 18 10 4.55 1 0.2 33 Example 19 10 3.03 1 0.3 22 Example 20 102.27 1 0.4 11 Example 21 10 1.82 1 0.5 0 Example 22 10 1.52 1 0.6 11Example 23 10 1.3 1 0.7 22 Example 24 10 1.14 1 0.8 32 Comparative 10 —1 — 45 Example 3

As shown in Table 14, in Examples 18 to 24, the variation amount(|ΔV_(DC_LC)|) of the DC voltage component V_(DC_LC) applied to theliquid crystal layer when changing the frame frequency was small andVcom shift was suppressed as compared with Comparative Example 3. Inparticular, Vcom shift was more suppressed in Examples 20 to 22.

(Evaluation 3-3)

In the display device of each of Examples 25 to 29 and ComparativeExample 4, the variation amount (|ΔV_(DC_LC)|) of the DC voltagecomponent V_(DC_LC) applied to the liquid crystal layer was calculatedwith a SPICE simulator when switching from the first frame frequency F₁(first driving period) to the second frame frequency F₂ (second drivingperiod) using the aforementioned image signal for driving. Table 15shows the simulation results.

TABLE 15 F₁ F₃ _(—) ₁ F₂ |ΔV_(DC) _(—) _(LC)| (Hz) (Hz) (Hz) X (mV)Example 25 4 2.67 1 0.3 25 Example 26 4 2 1 0.4 13 Example 27 4 1.6 10.5 0 Example 28 4 1.34 1 0.6 12 Example 29 4 1.14 1 0.7 24 Comparative4 — 1 — 38 Example 4

As shown in Table 15, in Examples 25 to 29, the variation amount(|ΔV_(DC_LC)|) of the DC voltage component V_(DC_LC) applied to theliquid crystal layer when changing the frame frequency was small andVcom shift was suppressed as compared with Comparative Example 4. Inparticular, Vcom shift was more suppressed in Examples 26 to 28.

(Evaluation 3-4)

In the display device of each of Examples 30 to 36 and ComparativeExample 5, the variation amount (|ΔV_(DC_LC)|) of the DC voltagecomponent V_(DC_LC) applied to the liquid crystal layer was calculatedwith a SPICE simulator when switching from the first frame frequency F₁(first driving period) to the second frame frequency F₂ (second drivingperiod) using the aforementioned image signal for driving. Table 16shows the simulation results.

TABLE 16 F₁ F₃ _(—) ₁ F₂ |ΔV_(DC) _(—) _(LC)| (Hz) (Hz) (Hz) X (mV)Example 30 2 1.9 1 0.35 23 Example 31 2 1.67 1 0.40 15 Example 32 2 1.481 0.45 8 Example 33 2 1.33 1 0.50 0 Example 34 2 1.21 1 0.55 7 Example35 2 1.11 1 0.60 15 Example 36 2 1.03 1 0.65 22 Comparative 2 — 1 — 25Example 5

As shown in Table 16, in Examples 30 to 36, the variation amount(|ΔV_(DC_LC)|) of the DC voltage component V_(DC_LC) applied to theliquid crystal layer when switching the frame frequencies was small andVcom shift was suppressed as compared with Comparative Example 5. Inparticular, Vcom shift was more suppressed in Examples 31 to 35.

The results of Evaluations 3-1 to 3-4 (Tables 13 to 16) show that Vcomshift when changing the frame frequency is more suppressed in the casewhere the frame frequencies satisfy a relation represented by thefollowing formula (1). In the following formula (1), F₃ corresponds toF_(3_1) (when the number of frame periods in the transition period is 1,F₃=F_(3_1)).

[Math.  11] $\begin{matrix}{0.4 \leq \frac{F_{1}F_{2}}{F_{3}\left( {F_{1} + F_{2}} \right)} \leq 0.6} & (1)\end{matrix}$

[Evaluation 4]

Evaluation was made for preferred relations of the frame frequenciesbetween the first driving period, the second driving period, and thetransition period in the case where the number of frame periods in thetransition period was an even number of 2 or greater (ClassificationExample 2). Specifically, in the display device of each of Examples 2and 37 to 46, the variation amount (|ΔV_(DC_LC)|) of the DC voltagecomponent V_(DC_LC) applied to the liquid crystal layer was calculatedwith a SPICE simulator when switching from the first frame frequency F₁(first driving period) to the second frame frequency F₂ (second drivingperiod) using the aforementioned image signal for driving. Table 17shows the simulation results. In Table 17, Y indicates values calculatedfrom the following formula (y).

[Math.  12] $\begin{matrix}{Y = \frac{\Sigma_{1}^{n}\left( {\frac{1}{F_{3\_ 2n}} - \frac{1}{F_{{3\_ 2n} - 1}}} \right)}{\frac{1}{F_{2}} - \frac{1}{F_{1}}}} & (y)\end{matrix}$

TABLE 17 F₁ F₃ _(—) ₁ F₃ _(—) ₂ F₃ _(—) ₃ F₃ _(—) ₄ F₂ |Δ V_(DC) _(—)_(LC)| (Hz) (Hz) (Hz) (Hz) (Hz) (Hz) Y (mV) Exam- 60 20 4 — — 1 0.20 30ple 37 Exam- 60 20 2.9 — — 1 0.30 20 ple 38 Exam- 60 20 2.25 — — 1 0.4010 ple 39 Exam- 60 10 2 — — 1 0.41 10 ple 44 Exam- 60 30 1 — — 0.5 0.493 ple 2 Exam- 60 20 1.87 — — 1 0.49 1 ple 40 Exam- 60 10 1.71 — — 1 0.491 ple 45 Exam- 60 45 30 90 1 0.5 0.50 1 ple 46 Exam- 60 20 1.57 — — 10.60 16 ple 41 Exam- 60 20 1.35 — — 1 0.70 24 ple 42 Exam- 60 20 1.2 — —1 0.80 32 ple 43

As shown in Table 17, in Examples 2 and 37 to 46, Vcom shift whenchanging the frame frequency was suppressed. In particular, Vcom shiftwas more suppressed in Examples 2, 39 to 41, and 44 to 46. This showsthat Vcom shift when changing the frame frequency is more suppressed inthe case where the frame frequencies satisfy a relation represented bythe following formula (2).

[Math.  13] $\begin{matrix}{0.4 \leq \frac{\Sigma_{1}^{n}\left( {\frac{1}{F_{3\_ 2n}} - \frac{1}{F_{{3\_ 2n} - 1}}} \right)}{\frac{1}{F_{2}} + \frac{1}{F_{1}}} \leq 0.6} & (2)\end{matrix}$

In the formula (2), n is an integer of 1 or greater.

[Evaluation 5]

Evaluation was made for preferred relations of the frame frequenciesbetween the first driving period, the second driving period, and thetransition period in the case where the number of frame periods in thetransition period was an odd number of 3 or greater (ClassificationExample 3). Specifically, in the display device of each of Examples 3 to6 and 47 to 52, the variation amount (|ΔV_(DC_LC)|) of the DC voltagecomponent V_(DC_LC) applied to the liquid crystal layer was calculatedwith a SPICE simulator when switching from the first frame frequency F₁(first driving period) to the second frame frequency F₂ (second drivingperiod) using the aforementioned image signal for driving. Table 18shows the simulation results. In Table 18, Z indicates values calculatedfrom the following formula (z).

[Math.  14] $\begin{matrix}{Z = \frac{\frac{1}{F_{3\_ 1}} + {\Sigma_{1}^{n}\left( {\frac{1}{F_{{3\_ 2n} + 1}} - \frac{1}{F_{3\_ 2n}}} \right)}}{\frac{1}{F_{2}} + \frac{1}{F_{1}}}} & (z)\end{matrix}$

TABLE 18 F₁ F₃ _(—) ₁ F₃ _(—) ₂ F₃ _(—) ₃ F₂ |Δ V_(DC) _(—) _(LC)| (Hz)(Hz) (Hz) (Hz) (Hz) Z (mV) Example 47 60 30 40 5 1 0.20 30 Example 48 6030 40 3.4 1 0.30 21 Example 49 60 30 40 2.5 1 0.40 10 Example 6 60 90 902 1 0.49 0 Example 5 60 30 30 1 0.5 0.50 2 Example 50 60 30 40 2 1 0.500 Example 3 120 5 40 3 1 0.50 0 Example 4 60 20 30 1 0.5 0.50 1 Example51 60 30 40 1.67 1 0.60 17 Example 52 60 30 40 1.42 1 0.70 26

As shown in Table 18, in Examples 3 to 6 and 47 to 52, Vcom shift whenchanging the frame frequency was suppressed. In particular, Vcom shiftwas more suppressed in Examples 3 to 6 and 49 to 51. This shows thatVcom shift when changing the frame frequency is more suppressed when theframe frequencies satisfy a relation represented by the followingformula (3).

[Math.  15] $\begin{matrix}{0.4 \leq \frac{\frac{1}{F_{3\_ 1}} + {\Sigma_{1}^{n}\left( {\frac{1}{F_{{3\_ 2n} + 1}} - \frac{1}{F_{3\_ 2n}}} \right)}}{\frac{1}{F_{2}} + \frac{1}{F_{1}}} \leq 0.6} & (3)\end{matrix}$

In the formula (3), n is an integer of 1 or greater.

[Evaluation 6]

In the display device of each of Examples 13 and 53 to 59 andComparative Examples 1 and 6 to 12, the variation amount (|ΔV_(DC_LC)|)of the DC voltage component V_(DC_LC) applied to the liquid crystallayer was calculated with a SPICE simulator when switching from thefirst frame frequency F₁ (first driving period) to the second framefrequency F₂ (second driving period) using the aforementioned imagesignal for driving. Tables 19 and 20 show the simulation results andFIG. 31 shows a graph of the simulation results. FIG. 31 is a graphshowing the results of simulation for display devices of Examples 13 and53 to 59 and Comparative Examples 1 and 6 to 12.

TABLE 19 F₁ F₃ _(—) ₁ F₂ |ΔV_(DC) _(—) _(LC)| (Hz) (Hz) (Hz) (mV)Example 53 60 40 30 <1 Example 54 60 24 15 <1 Example 55 60 17 10 <1Example 56 60 9.2 5 <1 Example 57 60 7.5 4 <1 Example 58 60 5.7 3 <1Example 59 60 3.9 2 <1 Example 13 60 2 1 <1

TABLE 20 F₁ F₃ _(—) ₁ F₂ |ΔV_(DC) _(—) _(LC)| (Hz) (Hz) (Hz) (mV)Comparative 60 — 30 2 Example 6 Comparative 60 — 15 3 Example 7Comparative 60 — 10 5 Example 8 Comparative 60 — 5 10 Example 9Comparative 60 — 4 12 Example 10 Comparative 60 — 3 17 Example 11Comparative 60 — 2 25 Example 12 Comparative 60 — 1 50 Example 1

As shown in Table 19 and FIG. 31, in Examples 13 and 53 to 59, thevariation in DC voltage component V_(DC_LC) applied to the liquidcrystal layer when changing the frame frequency was suppressed.Meanwhile, as shown in Table 20 and FIG. 31, in Comparative Examples 1and 6 to 12, the variation in DC voltage component V_(DC_LC) applied tothe liquid crystal layer when changing the frame frequency was large.Here, in Comparative Examples 1 and 6 to 12, the variation in DC voltagecomponent V_(DC_LC) applied to the liquid crystal layer was larger whenthe second frame frequency F₂ was 10 Hz or lower. In contrast, inExamples 13 and 53 to 59, the variation in DC voltage componentV_(DC_LC) applied to the liquid crystal layer was suppressed even whenthe second frame frequency F₂ was 10 Hz or lower. This shows that theeffects of the present invention can be exerted even when the framefrequency of the first frame frequency F₁ or the second frame frequencyF₂, whichever has a lower frame frequency, (in the present evaluation,the second frame frequency F₂) is 10 Hz or lower. Although thetransition period of each example included one frame period in thepresent evaluation, the similar effects were confirmed to be exertedeven when the transition period includes multiple frame periods.

Although the simulation was performed for an FFS mode liquid crystaldisplay device (Structure Example 1) in Evaluations 1 to 6, the similareffects were confirmed to be exerted in IPS mode, TN mode, or VA modeliquid crystal display devices (Structure Examples 2 to 4).

[Additional Remarks]

An aspect of the present invention may be a display device including: adisplay part including a common electrode; a driving part configured todrive the display part; and a display control part configured to controlthe driving part, the display control part being configured to performcontrol for AC drive of the display part, with a voltage applied to thecommon electrode defined as a reference and to provide a transitionperiod between a first driving period and a second driving period inswitching from the first driving period to the second driving period,the first driving period allowing the display part to be driven at afirst frame frequency, the second driving period allowing the displaypart to be driven at a second frame frequency different from the firstframe frequency, the transition period including a period where thedisplay part is driven at at least one frame frequency with a valuebetween the first frame frequency and the second frame frequency, thetransition period including, with a voltage applied to the commonelectrode defined as a reference, a positive period and a negativeperiod that last for different total durations, the positive periodallowing the display part to be driven at a positive voltage, thenegative period allowing the display part to be driven at a negativevoltage. This aspect can achieve a display device that can change theframe frequency with reduced flickers.

At least one period selected from the group consisting of the firstdriving period, the second driving period, and the transition period mayinclude a frame period including a refreshing period that refreshes ascreen of the display part and a pause period that is longer than therefreshing period and stops refreshing the screen of the display part.This structure (pause driving) achieves lower power consumption thandriving that performs refreshment only.

There may be a difference between polarity of the positive period or thenegative period in the transition period, whichever has a longer totalduration, and polarity of a frame period that belongs to the firstdriving period or the second driving period, whichever has a lower framefrequency, and is closest to the transition period. This structure canmore suppress Vcom shift when changing the frame frequency (switchingfrom the first frame frequency to the second frame frequency). Thisresults in better suppression of flickers.

The number of frame periods in the transition period may be 1. In thiscase, provided that F₁ represents the first frame frequency (unit: Hz),F₂ represents the second frame frequency (unit: Hz), and F₃ representsthe frame frequency (unit: Hz) in the transition period, the framefrequencies may satisfy the following formula (1). This structure canmore suppress Vcom shift when changing the frame frequency (switchingfrom the first frame frequency to the second frame frequency). Thisresults in better suppression of flickers.

[Math.  16] $\begin{matrix}{0.4 \leq \frac{F_{1}F_{2}}{F_{3}\left( {F_{1} + F_{2}} \right)} \leq 0.6} & (1)\end{matrix}$

The number of frame periods in the transition period may be an evennumber of 2 or greater. In this case, provided that F₁ represents thefirst frame frequency (unit: Hz), F₂ represents the second framefrequency (unit: Hz), and F_(3_1), F_(3_2), . . . , F_(3_2n−1), andF_(3_2n) represent frame frequencies (unit: Hz) in the transition periodin the order from a first driving period side to a second driving periodside, the frame frequencies may satisfy the following formula (2). Thisstructure can more suppress Vcom shift when changing the frame frequency(switching from the first frame frequency to the second framefrequency). This results in better suppression of flickers.

[Math.  17] $\begin{matrix}{0.4 \leq \frac{\Sigma_{1}^{n}\left( {\frac{1}{F_{3\_ 2n}} - \frac{1}{F_{{3\_ 2n} - 1}}} \right)}{\frac{1}{F_{2}} - \frac{1}{F_{1}}} \leq 0.6} & (2)\end{matrix}$

In the formula (2), n is an integer of 1 or greater.

The number of frame periods in the transition period may be an oddnumber of 3 or greater. In this case, provided that F₁ represents thefirst frame frequency (unit: Hz), F₂ represents the second framefrequency (unit: Hz), and F_(3_1), F_(3_2), . . . , and F_(3_2n), andF_(3_2n+1) represent frame frequencies (unit: Hz) in the transitionperiod in the order from a first driving period side to a second drivingperiod side, the frame frequencies may satisfy the following formula(3). This structure can more suppress Vcom shift when changing the framefrequency (switching from the first frame frequency to the second framefrequency). This results in better suppression of flickers.

[Math.  18] $\begin{matrix}{0.4 \leq \frac{\frac{1}{F_{3\_ 1}} + {\Sigma_{1}^{n}\left( {\frac{1}{F_{{3\_ 2n} + 1}} - \frac{1}{F_{3\_ 2n}}} \right)}}{\frac{1}{F_{2}} + \frac{1}{F_{1}}} \leq 0.6} & (3)\end{matrix}$

In the formula (3), n is an integer of 1 or greater.

The first frame frequency or the second frame frequency, having a lowerframe frequency, may have a frame frequency of 10 Hz or lower. Thisstructure can effectively suppress Vcom shift even when the lower framefrequency of the first frame frequency and the second frame frequency is10 Hz or lower.

The display part may further include a thin film transistor element, andthe thin film transistor element may include a semiconductor layerincluding an oxide semiconductor. This structure simultaneously achieveslow power consumption and high-speed driving.

The display device may be a liquid crystal display device. Thisstructure enables effective use of the present invention even when thedisplay device is a liquid crystal display device.

REFERENCE SIGNS LIST

-   1: Display device-   2: System control unit-   10: Display part-   11: Pixel-   12: Thin film transistor element-   13: Pixel electrode-   14: Common electrode-   20: Power generation circuit-   30: Display control circuit-   40: Scanning line drive circuit-   50: Signal line drive circuit-   60 a, 60 b, 60 c, 60 d: First substrate-   61: First alignment film-   62: Liquid crystal layer-   63: Second alignment film-   64 a, 64 b: Second substrate-   65: First supporting substrate-   66: First insulating film-   67: Second insulating film-   68: Black matrix-   69: Color filter-   70: Second supporting substrate-   GL1 to GLm: Scanning line-   SL1 to SLn: Signal line-   Cp: Pixel capacitance-   GCT: Scanning line control signal-   SCT: Signal line control signal-   Vcom: Common voltage-   EA₁, EA₂, EA₃, EB₁, EB₂, EB₃, EC₁, EC₂, EC₃, EC₄, ED₁: Erectric    field-   A1, A2, A3, B1, B2, B3, C1, C2, C3, C4, D1, D2: Circuit-   C₆₁: Capacitance of first alignment film-   C₆₂: Capacitance of liquid crystal layer-   C₆₃: Capacitance of second alignment film-   C₆₅: Capacitance of first supporting substrate-   C₆₆: Capacitance of first insulating film-   Cs: Storage capacitance-   R₆₁: Resistance of first alignment film-   R₆₂: Resistance of liquid crystal layer-   R₆₃: Resistance of second alignment film-   R₆₅: Resistance of first supporting substrate-   R₆₆: Resistance of first insulating film-   Rs: Resistance between pixel electrodes and common electrode-   F₁: First frame frequency-   F₂: Second frame frequency-   F₃, F_(3_1), F_(3_2), . . . , F_(3_2n−1), F_(3_2n), F_(3_2n+1):    Frame frequency in the transition period-   T_(p1), T_(n1), T_(n2), T₁, T₂, T₃, T_(3_1), T_(3_2), . . . ,    T_(3_2n−1), T_(3_2n), T_(3_2n+1): Length (time) of the frame period-   V_(DC_LC): DC voltage component applied to liquid crystal layer-   |ΔV_(DC_LC)|: Variation amount of DC voltage component applied to    liquid crystal layer

1. A display device comprising: a display part including a commonelectrode; a driving part configured to drive the display part; and adisplay control part configured to control the driving part, the displaycontrol part being configured to perform control for AC drive of thedisplay part, with a voltage applied to the common electrode defined asa reference and to provide a transition period between a first drivingperiod and a second driving period in switching from the first drivingperiod to the second driving period, the first driving period allowingthe display part to be driven at a first frame frequency, the seconddriving period allowing the display part to be driven at a second framefrequency different from the first frame frequency, the transitionperiod including a period where the display part is driven at at leastone frame frequency with a value between the first frame frequency andthe second frame frequency, the transition period including, with avoltage applied to the common electrode defined as a reference, apositive period and a negative period that last for different totaldurations, the positive period allowing the display part to be driven ata positive voltage, the negative period allowing the display part to bedriven at a negative voltage.
 2. The display device according to claim1, wherein at least one period selected from the group consisting of thefirst driving period, the second driving period, and the transitionperiod includes a frame period including a refreshing period thatrefreshes a screen of the display part and a pause period that is longerthan the refreshing period and stops refreshing the screen of thedisplay part.
 3. The display device according to claim 1, wherein thereis a difference between polarity of the positive period or the negativeperiod in the transition period, whichever has a longer total duration,and polarity of a frame period that belongs to the first driving periodor the second driving period, whichever has a lower frame frequency, andis closest to the transition period.
 4. The display device according toclaim 1, wherein the number of frame periods in the transition periodis
 1. 5. The display device according to claim 4, wherein, provided thatF₁ represents the first frame frequency (unit: Hz), F₂ represents thesecond frame frequency (unit: Hz), and F₃ represents the frame frequency(unit: Hz) in the transition period, the frame frequencies satisfy thefollowing formula (1): [Math.  1] $\begin{matrix}{0.4 \leq \frac{F_{1}F_{2}}{F_{3}\left( {F_{1} + F_{2}} \right)} \leq 0.6} & (1)\end{matrix}$
 6. The display device according to claim 1, wherein thenumber of frame periods in the transition period is an even number of 2or greater.
 7. The display device according to claim 6, wherein,provided that F₁ represents the first frame frequency (unit: Hz), F₂represents the second frame frequency (unit: Hz), and F_(3_1), F_(3_2),. . . , F_(3_2n−1), and F_(3_2n) represent frame frequencies (unit: Hz)in the transition period in the order from a first driving period sideto a second driving period side, the frame frequencies satisfy thefollowing formula (2): [Math.  2] $\begin{matrix}{0.4 \leq \frac{\Sigma_{1}^{n}\left( {\frac{1}{F_{3\_ 2n}} - \frac{1}{F_{{3\_ 2n} - 1}}} \right)}{\frac{1}{F_{2}} - \frac{1}{F_{1}}} \leq 0.6} & (2)\end{matrix}$ wherein n is an integer of 1 or greater.
 8. The displaydevice according to claim 1, wherein the number of frame periods in thetransition period is an odd number of 3 or greater.
 9. The displaydevice according to claim 8, wherein, provided that F₁ represents thefirst frame frequency (unit: Hz), F₂ represents the second framefrequency (unit: Hz), and F_(3_1), F_(3_2), . . . , F_(3_2n), andF_(3_2n+1) represent frame frequencies (unit: Hz) in the transitionperiod in the order from a first driving period side to a second drivingperiod side, the frame frequencies satisfy the following formula (3):[Math.  3] $\begin{matrix}{0.4 \leq \frac{\frac{1}{F_{3\_ 1}} + {\Sigma_{1}^{n}\left( {\frac{1}{F_{{3\_ 2n} + 1}} - \frac{1}{F_{3\_ 2n}}} \right)}}{\frac{1}{F_{2}} + \frac{1}{F_{1}}} \leq 0.6} & (3)\end{matrix}$ wherein n is an integer of 1 or greater.
 10. The displaydevice according to claim 1, wherein the first frame frequency or thesecond frame frequency, having a lower frame frequency, has a framefrequency of 10 Hz or lower.
 11. The display device according to claim1, wherein the display part further includes a thin film transistorelement, and the thin film transistor element includes a semiconductorlayer including an oxide semiconductor.
 12. The display device accordingto claim 1, wherein the display device is a liquid crystal displaydevice.